An antidepressant is the generic term for several classes of drugs used to treat various mood disorders--most commonly depression. Antidepressants do not have dependency risks, and second- and third-generation drugs have fewer side effects than their predecessors. While there are new debates among researchers about these drugs' effectiveness, use of antidepressants have steadily increased over the last decade. The use of these drugs by Americans doubled from 13 million in 1996 to 27 million in 2005, according to the Feb. 8, 2010, "Newsweek." The most commonly prescribed classes of antidepressants are SSRIs, SNRIs, MAOIs, and tricyclics. There are also a handful of additional types of drugs used as antidepressants.
SSRIs
Selective serotonin reuptake inhibitors (SSRIs) is the class of drugs mostly widely used to treat depression. Serotonin is a chemical in the brain used to transmit signals between neurons that helps regulate mood. An inadequate amount of this neurotransmitter is suspected to be one cause of depression. SSRIs work by inhibiting serotonin reuptake in presynaptic neurons in the brain. Types of SSRIs include fluoxetine, fluvoxamine, sertraline, paroxetine, escitalopram and citalopram.
Side effects are greatly reduced when compared with first-generation antidepressant drugs such as MAOIs and tricyclics, and side effects may diminish over time. Frequent side effects are restlessness, insomnia, weight loss or gain, sweating, dry mouth, decreased libido and fatigue. People taking SSRIs generally begin to see depression symptoms decrease in two months. Withdraw symptoms may also occur and they often include anxiety, agitation, tremors and nausea.
SNRIs
Serotonin-norepinephrine reuptake inhibitors (SNRIs) are a newer class of drugs that inhibit the reuptake of the neurotransmitters serotonin and norepinephrine. Norepinephrine neurotransmitters are involved in attention and arousal, and it activates areas in the brain called reward structures that increase and regulate behavior by inciting physical pleasure.This class of drugs includes desvenlafaxine, duloxetine, milnacipram and venlafaxine. SNRI medications have many of the same side effects and withdrawal symptoms as SSRIs. Mood increase generally occurs within the first two months as with SSRIs.
MAOIs
Monoamine oxidase inhibitors (MAOIs) were developed in the 1950s, making these drugs one of the oldest class of antidepressants. MAOIs work by preventing the neurotransmitters associated with mood---serotonin, norepinephrine and dopamine--from being metabolized by the enzyme monoamine oxidase.
Because of MAOIs' adverse food and drug interactions, they are generally not prescribed unless second- or third-generation antidepressants did not relieve symptoms. People who are prescribed MAOIs must practice dietary restrictions on foods that contain tyramine, which is a molecule that affects blood pressure. Because MAOIs also inhibit the metabolization of tyramine, consuming foods containing the molecule can cause dangerous levels of tyramine in the brain. These high levels can cause a sudden increase in blood pressure that can lead to a stroke. Foods with tyramine include chocolate, aged cheese, wine and pickled foods.
Other medications can also produce an adverse reaction in those taking MAOIs. Medications to avoid include other antidepressants, certain pain medications, decongestants and some weight-loss drugs. Taking additional antidepressants with MAOIs can cause dangerously high levels of serotonin in the brain, producing serotonin syndrome. Symptoms include confusion, hallucinations, seizures and an increased heart rate. People who experience these symptoms should seek immediate medical attention.
Side effects for MAOIs are similar to SSRIs, SNRIs, and tricyclics but may be more severe. Phenelzine and tranylcypromine are types of MAOIs.
Tricyclics
Tricyclics, also called TCAs, were the most commonly used antidepressants until the advent of SSRIs in the 1990s.Tricycles inhibit the absorption of both serotonin and norepinephrine and, to a lesser extent, dopamine.These drugs also block the action of other receptors such as histamine receptors and muscarinic acetylcholine receptors.These additional receptor blockages cause many of the adverse side effects that can occur while using TCAs.
Common side effects include dry mouth, dry nose, blurred vision, lowered gastrointestinal motility or constipation, urinary retention, cognitive impairment and increased body temperature. Side effects can be reduced if TCA dosage begins low and is gradually increased.
Withdrawal symptoms can occur if medication is suddenly discontinued. Types of TCAs include amitriptyline, amoxapine, desipramine, doxepin, imipramine, nortriptyline, protriptyline and trimipramine.
Additional Drugs
Noradrenergic and specific serotonergic antidepressants (NaSSAs) include the drugs mianserin and mirtazapine. People taking NaSSAs often experience an increased appetite and weight gain.
Norepinephrine (noradrenaline) reuptake inhibitors (NRIs) restrict the absorption of neurotransmitters norepinephrine and epinephrine. NRIs include atomoxetine/tomoxetine, mazindol, reboxetine and viloxazine.
Norepinephrine-dopamine reuptake inhibitors (NDRIs) restrict the reuptake of norepinephrine and dopamine. Bupropion is the most commonly prescribed NDRI.
Selective serotonin reuptake enhancers (SSREs) is a class of drugs that enhances the reuptake of serotonin rather than inhibiting it. Tianeptine is a type of SSRE. This class of drugs is thought to have fewer side effects than SSRIs, especially sexual side effects.
Melatonergic agonists is a class of drugs that works similarly to SSRIs and SNRIs but with fewer of the side effects associated with these drugs. Melatonergic agonists include agomelatine.
Trazodone may also be used as an antidepressant. The medication is part of the piperazine and triazolopyridine chemical classes. Because of its sedative effect it is also used with other antidepressants to help people experiencing insomnia.
Buspirone is often used in the treatment of anxiety, but has been known to be used in treating depression. Unlike benzodiazepines, which are also often used to treat anxiety, buspirone does not have a risk of dependency or addition. Buspirone is part of the piperazine and azapirone chemical classes.
